There it is...the Question for the day!

I aquired a 383 shortblock with forged pistons and rods with a scat crank. This motor has an 11.8:1 setup, which I felt was high, but I got a killer deal for it. I know I see people in the 11-11.5 range every now and again...but is 11.8 too high?

Now-- I have been told that this will run fine on 93 octane fuel, but If I spray it at the track to put a quality octane booster in the tank. SO----I lay it out for you guys!

ASSUMING a proper programming, How much compression can you get away with on Premium Gasoline????

 

A buddy of mine Jason Short was running 12:1 or greater on pump gas with no problem.

 

96Z- I read you Dyno #'s thread...awesome bro! thanks for replying. I am prolly gonna call Bauer soon and talk with those guys.

 

Sweet, Yeah Bret is a great guy and really knows his stuff. Im tremendously happy with the work he has done. Now I just gotta find some way to put it too the ground.

11.8:1 should be no prob on 93.

 

I have seen many people with compression as high as 12.1 running pump gas (93) with no detonation with a GOOD tuning, granted the person is staying N/A.

However, upper RPM power is boosted very well by Race gas, such as 100 octane. I tried 100 Octane in my car, and the power increase from 4000 RPM to 6200 RPM was definitely noticeable. I did feel a loss from 2000 to 3500 though.

 

WheelmanZ28- will the 100 octane mess with the O2's? I could run race fuel at the track IF I do spray it, but was concerned about O2 damage.

BTW- the initial tune will be a Ed Wright tune..then I may have it Dynotuned at Thunder Racing later.

 

Actually, you are all "wrong" in a sense. Not saying that whoever doesn't run whatever but- thats completely irrelivant


static compression (the compression you are discussing- basically volume at the bottom of the stroke / volume at TDC- is completely useless independantly.

The compression that will tell you if you will detonate is dynamic compression ratio. Your cam timing and overlap the main factors of this.

as a general rule of thumb "larger cams bleed off more compression" so you can run more static compression in order to attain the desired static compression ratio.

Stick a hotcam in motor and it will go kaboom.

for calculators are more indepth explanations do a search in advanced tech. Mr. Horsepower has already answered your questions in great detail.

so use a calculator

and what cam BTW

 

The answer to that question is Yes and No...

If the racing gas is LEADED racing gas, then YES, it will damage your O2 sims.

However, there are many places that sell racing gas that isn't straight LEADED. Make sure the gas its straight octane/gas mix and not leaded before u pump.

 

Trey- I will go search it...I am WAY undecided on the cam...right now I may be buying a beater, in which case it would be more viable to go radical, but right now it is my main means of transportation. But none the less, it will have considerably more cam than a hotcam. I am thinking GTP-6 or 8 range, I am gonna call a few companies and explain my set up...maybe a custom grind. I am thinking that the xtreme 230/236 is the lowest I'd consider.

Wheelman- Yeah that is what I thought.

I am still getting the Top End of the engine worked out..Head still need to get portwork and valvetrain/cam setup to decide on...I really want to build it right to start with.

 

OK- after reading several CR related topics, and the totural on DCR I gathered that I should be good with anything(for the most part) from the CC306 and up, which I am pretty certain that that will happen.

 

not entirely true Trey, did you have a motor that you built with a hotmcam and that compression that came appart?

i was involved in tuning a 396 12:1 motor with a teeny cam.. hot camstyle, with no problems on pump gas.


it had much steeper ramps than a hot cam, but similar idle characteristics(NO lope, none, nada).

 

i havn't had it together with this cam in there
this cam has tons of overlap but who knows what would happen


nonetheless wory about dynamic

 

VP and Sunoco both offer 100+ octane unleaded race gas.

 

My 94 has a 383 with 12:1, I run pump gas, it has about 3500 miles on the motor with no problems, however my buddy with a 351w stroked to 393 is running 11.5:1 and has to run 104 racing fuel. He didn't when he got the car and his motor blew up at the track,
ran 13.4 @ 84 MPH, I would run 5 gallons of racing fuel mixed with whatevers in the tank and see how that does.

 

11.8 is not too high, depending on the cam.

I am running about 11.8:1 on __91__ octane California MTBE gas. I am also running a Comp XE 230/236-112 cam. The heads were milled 0.030", and I used the Impala LT1 head gaskets. According to the calculator I have, the DCR is about 9.0:1, which is not that much more than the stock figures I have seen. Now, I would suppose that using a smaller cam could cause problems, especially since I have to run 91 octane. I can't get anything else without going to race fuels here in CA.

BRAD